Various forms of embodiment of yarn supply apparatus are known in the art for feeding yarn in a slip-free or positive manner, having a yarn storage or supply drum driven by a drive source such as a perforated belt. Supply windings or loops of yarn, comprising a plurality of windings located beside one another, are retained on the drum. In order to assure a neatly wound yarn supply in which storage loops are located beside one another in an orderly pattern, the storage loops, from one end of which yarn is drawn off continuously, must be axially displaced on the storage drum toward the yarn run-off side at the same rate as yarn is delivered to the storage loops on the run-on or supply side. In storage drums which have a cylindrical circumferential surface, the drums require their own feed apparatuses (such as that disclosed in U.S. Pat. No. 4,138,866, to which German Patent No. 26 08 590, corresponds). Although these feed apparatuses do assure a satisfactory axial advancement or feed of the storage loops for all types of yarns and threads in practical use, still they represent an additional expense, aside from the fact that they also require a certain amount of maintenance.
Yarn supply or feed apparatuses have therefore become known in which by means of a particular shaping of the profile of the storage drum, an automatic axial feed of the storage loops on the drum is attained, so that a separate, additional feed device cooperating with the drum or with the windings located on it can be dispensed with. In a storage drum of this type (U.S. Pat. No. 2,613,273, to which German Patent Disclosure Document DE-OS No. 26 13 273 corresponds), a yarn run-on or supply zone which curves continuously inward is provided, on which the yarn runs on at a tangent and which gradually merges into a slightly conical transitional zone, which in turn joins a cylindrical circumferential surface of the drum. This embodiment of the storage drum does result in an axial feeding or advancement of the storage loops; however, when it is used for various yarns it cannot be precluded that with some types of yarn the windings of the storage loops will tangle or drop off, impairing the run-off of the yarn, thereby causing nonuniform yarn supply and yarn breakage.
In a yarn storage and supply apparatus having a storage drum of basically similar embodiment (U.S. Pat. No. 4,180,215, to which German Published Application DE-AS No. 27 43 749 corresponds), which has on its circumference a support surface, receding in an inward curve from the yarn delivery location, for a plurality of yarn windings located beside one another, the arrangement was therefore chosen such that the support surface of the storage drum extends with a continuous curvature from the initial surface, which recedes inward, to a final zone, which widens outward toward the yarn draw-off side and at the end of which zone the diameter of the storage drum is larger than at its end on the yarn run-in side. However, because of the continuously curved shape of the support surface, this storage drum operates with a certain slip between the yarn and the storage drum. In man-made monofilamentary yarns, for instance, this causes a certain wearing of the support surface, with the result that the circumferential surface of the storage drum must be provided with an absolutely smooth and wear-resistant surface, which in turn makes the manufacture of the storage drum substantially more expensive.